The present invention disclosed herein relates to a target for generating ions and a treatment apparatus using the target, and more particularly, to a target for generating protons or carbon ions and an ion beam treatment apparatus using the target.
Methods for radiotherapy may include X-ray treatments, electron beam treatments, and ion beam treatments. Of these, the X-ray treatments are the lowest-cost treatment methods using the simplest device and are thus being most commonly used at the present day. Although it has been proven in 1950's that tumors can be treated by accelerating electrons using an accelerator to inject the electrons into the tumors, the electron beam treatments had not been taken over as one method for radiotherapy until electron accelerators were miniaturized in 1980's. In the X-ray treatments or the electron beam treatments, hydrogen bonds within cancer cells can be cut to destroy DNAs of the cancer cells. However, side effects in which healthy cells existing within the traveling path of X-rays or electron beams are seriously damaged may occur. Technologies such as intensity-modulated radiation therapy (IMRT), tomo therapy, and cyber knife have been developed as methods for reducing the radiation exposure of normal cells. However, the technologies cannot completely solve the above-described side effects.
The ion beam treatments are in the spotlight as treatment methods which can mitigate the side effects due to the X-ray treatments or the electron beam treatments. To allow the ion beam to penetrate a material, the ion beam should be accelerated to have high velocity, like the electrons. Even though the ion beam is gradually decreased in velocity when the ion beam penetrates a certain material, the ion beam is subject to the most energy loss of ionizing radiation just before the ion beam is stopped. This phenomenon is called a Bragg peak after William Henry Bragg, which discovered the phenomenon in 1903. Thus, in a case of such an ion beam treatment, malignant tumors may be selectively and locally treated when the ions are precisely controlled in velocity. When tumors are disposed at a deep position of the human body, protons or ions should be accelerated to a significantly high energy level at the outside of the human body. Methods of accelerating protons or ions may include a laser driven ion acceleration method. When high-power laser beam is emitted to a thin film, ions or protons within the thin film may escape with acceleration energy by a target normal sheath acceleration model (TNSA model) or a radiation pressure acceleration model (RPA model). After that, the ions may penetrate the body of a patient according to the acceleration energy to stop at a predetermined depth corresponding to the location of a tumor, and a large amount of free oxygen radicals may be generated at the predetermined depth to necrotize the tumor cells, which is a general principle of the ion beam treatment.
Ions, used in the ion beam treatment using the laser driven ion acceleration method, have the following two properties. First, the ions should have high energy to arrive at a deep portion of a human body. Secondly, most of the ions should have substantially the same energy. Protons, having an energy level of about 250 MeV, can arrive at a portion located at a depth of about 20 cm in a human body. For example, ions having a high energy level of about 70 MeV may be used in a retinoblastoma treatment, and ions having a high energy level of about 200 MeV or higher may be used to treat a caner in a deep portion of a human body.
In addition, most of the protons or ions generated using a femtosecond laser should have uniform energy. Otherwise, ions may not be collected only in a tumor region. Accordingly, a normal tissue located out of the tumor region may be exposed to radiation.
In order to satisfy the two properties of ions, a target as an ion source should have a significantly small thickness. Thus, the target should be an ultra thin film.
In addition, a laser for accelerating the ions should have a significantly high energy of about 1019 to 1021 W/cm2. This requires a significantly large laser system and high costs.